Inhibition of aqueous systems from deposition of scale

ABSTRACT

The deposition of scale-forming salts from an aqueous system containing a scale-forming amount of a salt such as calcium carbonate, calcium sulfate, barium sulfate, strontium sulfate, strontium carbonate and magnesium carbonate is inhibited by adding to the system an effective amount of triorthophosphate ester of trimethylol propane and the alkali metal and ammonium salts thereof. The aqueous system is suitably a brine in a subsurface formation to which the inhibitor is added.

United States Patent DePierri, Jr.

[ Feb. 22, 1972 [54] INHIBITION OF AQUEOUS SYSTEMS FROM DEPOSITION OF SCALE [72] lnventor: William G. DePierri, Jr., Baytown, Tex. [73] Assignee: Esso Research and Engineering Company [22] Filed: July 10, 1970 [2]] Appl. No.: 54,014

Related US. Application Data [62] Division of Ser. No. 718,901, Apr. 4, 1968.

Tate ..2 l0/58 X Vogelsang ..210/58 Primary Examiner-l-lerbert B. Guynn Attorney-Thomas B. McCulloch, Timothy L. Burgess, Melvin F. Fincke, John S. Schneider, Sylvester W. Brock, Jr. and Kurt S. Myers 57] ABSTRACT The deposition of scale-forming salts from an aqueous system containing a scale-forming amount of a salt such as calcium carbonate, calcium sulfate, barium'sulfate, strontium sulfate, strontium carbonate and magnesium carbonate is inhibited by adding to the system an effective amount of triorthophosphate ester of trimethylol propane and the alkali metal and ammonium salts thereof. The aqueous system is suitably a bn'ne in a subsurface formation to which the inhibitor is added.

7 Claims, No Drawings INHIBITION OF AQUEOUS SYSTEMS FROM DEPOSITION OF SCALE CROSS-REFERENCE TO RELATED APPLICATION This application is a division of U.S. Ser. No. 718,901, filed Apr. 4, 1968, for William G. DePierri, Jr. entitled Inhibition of Aqueous Systems From Deposition of Scale."

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is directed to the prevention of scale which deposits from an aqueous system. More particularly, the invention is concerned with the inhibition of an aqueous system containing calcium carbonate, strontium carbonate, magnesium carbonate, calcium sulfate, barium sulfate and strontium sulfate, and other water-insoluble salts. In its more specific aspects, the invention is concerned with the inhibition of the deposition of water-insoluble salts in formations containing said salts.

2. Description of the Prior Art It has been known heretofore to use phosphorous compounds in inhibition of scale in aqueous systems. It has also been known to introduce into subsurface formations compounds of phosphorous to prevent deposition of water-insoluble salts. However, the prior art has not been satisfactory in that either the salts would not remain in the subsurface formation when injected thereinto such as by failure of the salts to absorb on the formation rock or the injected inhibitor would lose its effectiveness. The present invention specifically overcomes the limitations of the prior art.

The following specific U.S. Pat. Nos. were considered with respect to this invention: 2,128,161, 3,213,017, 3,258,071, 3,258,428, 3,271,306, 3,283,817, 3,288,217, 3,304,349, 3,308,161, 3,336,221.

SUMMARY OF THE INVENTION The present invention may be briefly described and summarized as involving a new compound which is the triorthophosphate ester of trimethylol propane and the alkali metal and ammonium salts thereof. Specifically the present invention involves the following compound:

The alkali metal and ammonium salts of the phosphate ester of trimethylol propane are also part of this invention. The invention may also be briefly summarized as involving inhibition of the deposition of scale from an aqueous system such as a brine containing salts of calcium carbonate, calcium sulfate, barium sulfate, strontium sulfate, strontium carbonate and magnesium carbonate by adding the triorthophosphate ester of trimethylol propane and the alkali metal and ammonium salts thereof to the aqueous system which may be conveniently accomplished by introducing the particular compound under pressure into the subsurface formation.

DESCRIPTION OF THE PREFERRED MODE AND EMBODIMENT In accordance with the present invention an inhibitor which is effective in preventing the precipitation of calcium carbonate, strontium carbonate, magnesium carbonate, barium sulfate and strontium sulfate from supersaturated solutions has been provided. In accordance with the present invention this inhibitor is prepared by the phosphorylation of trimethylol propane as outlined in the following equation:

CHzOH CHzOPOsHz (IIIzClIz-C-CHaOII 3H3PO4 CHaCHz-C-CHzOPOaHz 3Hz0 (III OII CIIzOPOaIIe A B C The inhibitor which is the triorthophosphate ester of trimethylol propane may suitably be used in the acid form or it may be neutralized, either partially or completely, with a base such as sodium hydroxide, potassium hydroxide, ammonia, and the like and the salt thus formed used.

In order to illustrate the effectiveness of the present invention, the inhibitor of the present invention was added to a carbonated solution and the results of these several operations are shown in the following Table I which sets out the percent inhibition, the concentration and the analysis of the aqueous system containing calcium carbonate.

TABLE I Inhibition with Carbonatelnhibitor (C)' Concentration 1' Inhibition Blank 0 L5 p.p.m. 3 p.p.m. 6 p.p.m I2 p.p.m.

mAuN

The test were run at 150 F. for 20 Hrs.

The inhibitor is prepared in accordance with the foregoing equation. Thus, in a specific example 0.68 moles of trimethylol propane were mixed with 4.1 moles of l 15 percent polyphosphoric acid; a rapid exothermic reaction resulted when stirring was started in which the temperature rose to 103 C. After the exothermic reaction ended after about 5 minutes, the reaction mixture was heated for about 1 hour with stirring at a temperature of l05-l 12 C. The inhibitor of the present invention was recovered as a viscous brown liquid and was used in the concentrations and operations set out in Table 1, supra.

Temperatures employed in preparing the inhibitor may range from about 60 C. to C. It is preferred to use a molar excess of polyphosphoric acid in the practice of the present invention; thus, while about 3 moles of polyphosphoric acid may be used per mole of trimethylol propane, it is preferred to use about 6 moles. Thus, from about 3 to about 10 moles of polyphosphoric acid per mole of trimethylol propane may be used.

As another example of the present invention, the inhibitor prepared as described supra was used in a brine containing 5 percent by weight NaCl and 500 p.p.m. of barium sulfate. This was compared with an uninhibited solution where the uninhibited solution gave a precipitate of barium sulfate upon mixing while the solution containing 10 p.p.m. of inhibitor remained clear for over 2 hours.

In another operation where 3 p.p.m. of inhibitor was added to the same solution the precipitate began to form after about 30 minutes. Thus, it is contemplated in the present invention that depending on the particular salt in the aqueous system the inhibitor may be used in a concentration ranging from about 1 p.p.m. up to about 50 p.p.m.; for the barium sulfate and strontium sulfate supra the range may be from about 1 p.p.m. up to about 25 p.p.m.

It is indeed a surprise that such small amounts of inhibitor would be effective in preventing the deposition of the particular water-insoluble salts.

The present invention is quite advantageous and useful and may be used in various aqueous systems such as oil wells, wells containing brine, salt water disposal systems, in water-treatin g plants and the like where the system is not exposed to temperatures in excess ofabout 200 F.

The nature and objects of the present invention having been completely described and illustrated and the best mode and embodiment contemplated set forth.

What I wish to claim as new and useful and secure by Letters Patent is:

l. A method of inhibiting the deposition of scale forming salts from an aqueous system containing a scale-forming amount of a water-insoluble salt selected from the group consisting of calcium carbonate, calcium sulfate, barium sulfate, strontium carbonate, strontium sulfate and magnesium carbonate which comprises:

adding to said system an effective amount of a compound selected from the group consisting of:

and the alkali metal and ammonium salts thereof. 2. A method in accordance with claim 1 in which the compound is:

CH2O POaHz CH3CH2CCH2O POaHz CHzO PO H and the water-insoluble salt is calcium carbonate. 3. A method in accordance with claim 1 in which the compound is:

CH O P OaHz CHaCH2(3CHzO P 03112 01120 P CH2 5 and the water insoluble salt is barium sulfate.

4. A method in accordance with claim I in which the compound is:

CHzO P 03H:

CIhCHr-C-CHzO P0311:

CHzO P 03112 and the water-insoluble salt is strontium sulfate.

5. A method in accordance with claim 4 in which the aqueous system is a brine in a subsurface formation and the compound is introduced into the subsurface formation.

6. A method in accordance with claim 4 in which the effective amount is within the range from about 1 to about 50 p.p.m. of the aqueous system.

7. A method in accordance with claim 1 in which the compound is:

and the water insoluble salt lS calcium sulfate. 

2. A method in accordance with claim 1 in which the compound is: and the water-insoluble salt is calcium carbonate.
 3. A method in accordance with claim 1 in which the compound is: and the water insoluble salt is barium sulfate.
 4. A method in accordance with claim 1 in which the compound is: and the water-insoluble salt is strontium sulfate.
 5. A method in accordance with claim 4 in which the aqueous system is a brine in a subsurface formation and the compound is introduced into the subsurface formation.
 6. A method in accordance with claim 4 in which the effective amount is within the range from about 1 to about 50 p.p.m. of the aqueous system.
 7. A method in accordance with claim 1 in which the compound is: and the water insoluble salt is calcium sulfate. 